E. Dale Broder

Predator-Induced Phenotypic Plasticity in Metabolism and Rate of Growth: Rapid Adaptation to a Novel Environment

Novel environments often impose directional selection for a new phenotypic optimum. Novel environments, however, can also change the distribution of phenotypes exposed to selection by inducing phenotypic plasticity. Plasticity can produce phenotypes that either align with or oppose the direction of selection. When plasticity and selection are parallel, plasticity is considered adaptive because it provides a better pairing between the phenotype and the environment. If the plastic response is incomplete and falls short of producing the optimum phenotype, synergistic selection can lead to genetic divergence and bring the phenotype closer to the optimum. In contrast, non-adaptive plasticity should increase the strength of selection, because phenotypes will be further from the local optimum, requiring antagonistic selection to overcome the phenotype-environment mismatch and facilitate adaptive divergence. We test these ideas by documenting predator-induced plasticity for resting metabolic rate and growth rate in populations of the Trinidadian guppy (Poecilia reticulata) adapted to high and low predation. We find reduced metabolic rates and growth rates when cues from a predator are present during development, a pattern suggestive of adaptive and non-adaptive plasticity, respectively. When we compared populations recently transplanted from a high-predation environment into four streams lacking predators, we found evidence for rapid adaptive evolution both in metabolism and growth rate. We discuss the implications for predicting how traits will respond to selection, depending on the type of plasticity they exhibit.

Gene Flow Constrains and Facilitates Genetically Based Divergence in Quantitative Traits

Theory predicts that gene flow will decrease phenotypic differences among populations. Correlational studies have in some cases documented constraining effects of gene flow on phenotypic divergence and/or have also provided evidence for local differentiation despite high gene flow. However, correlative studies are unable to evaluate how gene flow affects genetically based phenotypic divergence or the extent to which gene flow constrains adaptive divergence. Translocation experiments using Trinidadian guppies provided an opportunity to test the effects of new gene flow on quantitative traits in native recipient populations. We measured a suite of traits in guppies reared in common garden environments before and multiple generations following gene flow from guppies that originated from a different environment. We interpreted our results in light of a priori predictions based on evolutionary theory and extensive background information about guppies and our focal populations. Although we could not include a spatiotemporal control that would allow us to be certain that the observed changes were directly caused by gene flow, we found that post-gene flow populations showed genetically based shifts in most traits. Whether traits shifted in predicted adaptive directions or whether they became more or less similar to the source population depended on the trait and initial conditions of the population. Our study provided a rare opportunity to test how recent gene flow affects genetically based changes in traits with known adaptive significance, and our results attest to the complex interactions between gene flow and selection.

A slow-growth high-mortality meta-analysis for insects: A comment on Chen & Chen

Insect Science recently published a meta-analysis that tried to test support for the slow-growth high-mortality (hereafter SG-HM) hypothesis (Chen & Chen, 2018). Meta-analysis is a powerful statistical tool used to quantitatively compare and summarize multiple studies (Arnqvist & Wooster, 1995). However, results from a meta-analysis must be carefully interpreted when only limited sample sizes are available. Many conclusions made by Chen and Chen (2018) are based on low sample sizes and/or have small fail-safe numbers, which is problematic when making conclusions about whether the SG-HM hypothesis is supported or rejected. The SG-HM hypothesis is based on the idea that development time of an herbivorous insect impacts its survival and thus also its fitness. The longer an insect feeds on a plant, the longer it is exposed to natural enemies (i.e., predators, parasitoids, and pathogens) or adverse climatic events, which increases its risk of mortality. Feeny (1976) first proposed that herbivores take more time to develop when they feed on low-quality plants (e.g., high chemical/physical defenses or low nutritional quality) than when they feed on high-quality plants, which presumably reduces herbivore fitness. Later, Price et al. (1980) predicted that the longer an herbivore in a vulnerable immature stage takes to develop into a reproductive adult, the greater the risk of attack by natural enemies; if an immature insect dies before reaching reproductive maturity, then fitness is reduced to zero. The SG-HM hypothesis has now been tested many times with studies both supporting or rejecting it for various reasons (e.g., Damman, 1987; Haggstrom & Larsson, 1995; Benrey & Denno, 1997; Fordyce & Shapiro, 2003; Lill & Marquis, 2001; Murphy, 2004; Medina et al., 2005; Cornlissen & Stiling, 2006),

Purring Crickets: The Evolution of a Novel Sexual Signal

Opportunities to observe contemporary signal change are incredibly rare but critical for understanding how diversity is created and maintained. We discovered a population of the Pacific field cricket (Teleogryllus oceanicus) with a newly evolved song (purring), different from any known cricket. Male crickets use song to attract females from afar and to court females once near. Teleogryllus oceanicus is well known for sexual signal evolution, as exemplified by a recent signal loss. In this study, we characterized the new purring sound and investigated the role of the purr in long-distance and short-distance communication. The purring sound differed from typical ancestral calls in peak frequency, amplitude, and bandwidth. Further, the long-distance purring song facilitated mate location, though the role of courtship purring song is less clear. Our discovery of purring male crickets is an unprecedented opportunity to watch the emergence of a newly evolved sexual signal unfold in real time and has potential to illuminate the mechanisms by which evolutionary novelties arise and coevolve between the sexes.

Geographic variation in responses of European yellow dung flies to thermal stress

Climatic conditions can be very heterogeneous even over small geographic scales, and are believed to be major determinants of the abundance and distribution of species and populations. Organisms are expected to evolve in response to the frequency and magnitude of local thermal extremes, resulting in local adaptation. Using replicate yellow dung fly (Scathophaga stercoraria; Diptera: Scathophagidae) populations from cold (northern Europe) and warm climates (southern Europe), we compared 1) responses to short-term heat and cold shocks in both sexes, 2) heat shock protein (Hsp70) expression in adults and eggs, and 3) female reproductive traits when facing short-term heat stress during egg maturation. Contrary to expectations, thermal traits showed minor geographic differentiation, with weak evidence for greater heat resistance of southern flies but no differentiation in cold resistance. Hsp70 protein expression was little affected by heat stress, indicating systemic rather than induced regulation of the heat stress response, possibly related to this fly groups preference for cold climes. In contrast, sex differences were pronounced: males (which are larger) endured hot temperatures longer, while females featured higher Hsp70 expression. Heat stress negatively affected various female reproductive traits, reducing first clutch size, overall reproductive investment, egg lipid content, and subsequent larval hatching. These responses varied little across latitude but somewhat among populations in terms of egg size, protein content, and larval hatching success. Several reproductive parameters, but not Hsp70 expression, exhibited heritable variation among full-sib families. Rather than large-scale clinal geographic variation, our study suggests some local geographic population differentiation in the ability of yellow dung flies to buffer the impact of heat stress on reproductive performance.

Forest Fire Severity Affects Host Plant Quality and Insect Herbivore Damage

Abstract Climate change models predict increased forest fire occurrence and severity in the near future. Forest fire disturbance affects multiple ecological interactions, but there is little evidence for how naturally-occurring fires affect plant quality and herbivore damage, which is important because plants and herbivorous insects comprise most of the diversity in natural ecosystems and are responsible for a variety of ecosystem services. We surveyed three fires in the Rocky Mountains to investigate the effects of fire severity on wax currant (Ribes cereum), an important source of food and cover for wildlife in Colorado. We measured plant quality and herbivore damage; we found that fire severity had a significant negative effect on both measures. Notably, high severity fires decreased herbivore damage by about 50%. Furthermore, we found that the effect of fire on insect herbivore damage is mostly direct, but that indirect effects mediated through changes in plant quality are also significant. Our results have important implications for the effects of climate-driven increases in fire severity on plant-insect interactions, illustrating strong direct and weaker indirect negative effects of fire severity in a forest ecosystem.

An experimental test of alternative population augmentation scenarios: Population Augmentation

Human land use is fragmenting habitats worldwide and inhibiting dispersal among previously connected populations of organisms, often leading to inbreeding depression and reduced evolutionary potential in the face of rapid environmental change. To combat this augmentation of isolated populations with immigrants is sometimes used to facilitate demographic and genetic rescue. Augmentation with immigrants that are genetically and adaptively similar to the target population effectively increases population fitness, but if immigrants are very genetically or adaptively divergent, augmentation can lead to outbreeding depression. Despite well-cited guidelines for the best practice selection of immigrant sources, often only highly divergent populations remain, and experimental tests of these riskier augmentation scenarios are essentially nonexistent. We conducted a mesocosm experiment with Trinidadian guppies (Poecilia reticulata) to test the multigenerational demographic and genetic effects of augmenting 2 target populations with 3 types of divergent immigrants. We found no evidence of demographic rescue, but we did observe genetic rescue in one population. Divergent immigrant treatments tended to maintain greater genetic diversity, abundance, and hybrid fitness than controls that received immigrants from the source used to seed the mesocosms. In the second population, divergent immigrants had a slightly negative effect in one treatment, and the benefits of augmentation were less apparent overall, likely because this population started with higher genetic diversity and a lower reproductive rate that limited genetic admixture. Our results add to a growing consensus that gene flow can increase population fitness even when immigrants are more highly divergent and may help reduce uncertainty about the use of augmentation in conservation.

Small Fish, Big Questions: Inquiry Kits for Teaching Evolution

Abstract Evolution education poses unique challenges because students can have preconceptions that bias their learning. Hands-on, inquiry approaches can help overcome preset beliefs held by students, but few such programs exist and teachers typically lack access to these resources. Experiential learning in the form of self-guided kits can allow evolution education programs to maximize their reach while still maintaining a high-quality resource. We created an inquiry-based kit that uses live Trinidadian guppies to teach evolution by natural selection using the VIST (Variation, Inheritance, Selection, Time) framework. Our collaborative team included evolutionary biologists and education specialists, and we were able to combine expertise in evolution research and inquiry-based kit design in the development of this program. By constructing the kits with grant funds slated for broader impacts and maintaining them at our universitys Education and Outreach Center, we made these kits freely available to local schools over the long term. Students and teachers have praised how clearly the kits teach evolution by natural selection, and we are excited to share this resource with readers of The American Biology Teacher.

Teaching Evolution Using Live Animals and Inquiry-Based, Self-Guided Kits

The authors describe their experiences with evolution and science education and how this led to their interest in inquiry-based teaching. Inquiry-based evolution education programs should be effective but are relatively uncommon, likely because of the resources and expertise required to create them. University/K-12 collaborations may be a solution but tend to be limited in their reach. Kit-based teaching allows inquiry-based evolution programs to be more broadly disseminated. Kits may also improve engagement and science self-efficacy since students take ownership of their learning and independently master science tasks. We describe an inquiry-based kit that we developed in collaboration with local teachers and an Education and Outreach Center at Colorado State University. We used three populations of locally adapted fish, Trinidadian guppies, to illustrate important concepts in evolution. Students work through the self-guided kit and booklet to complete inquiry and authentic science experiments and observations. These activities allow them to discover each concept and the definition of evolution at the end of the program. We describe the kit in detail and reflect on the challenges and successes associated with its creation and implementation.

The Study of Animal Behavior Provides Valuable Opportunities for Original Science Fair Projects: Recommendations from The Animal Behavior Society, Education Committee

Abstract The study of Animal Behavior is critically important in understanding our living world and is a major program within the NSF. For students, animal behavior projects offer the opportunity to explore original questions in a scientifically rigorous manner. However, animal behavior projects are under-represented in science fairs and are often discouraged by teachers and judges. We give a sample of the types of questions that students could explore and we suggest appropriate judging criteria.